Downhole tension swivel sub

ABSTRACT

A downhole equipment for use in the gas and oil drilling industry includes a first elongate member arranged in telescopic relation with a second elongate member, the elongate members being moveable relative to one another between a retracted position in which at least one tooth provided on the first elongate member is engaged with at least one tooth provided on the second elongate member so as to prevent relative rotation therebetween, and an extended position in which the at least one tooth of the second elongate member so as to permit relative rotation between the elongate members and in which abutment surfaces of the elongate members are in mechanical communication with each other so as to prevent further extending telescopic movement, Thus, the apparatus may be located between a spear and rotary easing cutter for setting the spear and for holding a casing and cutting string in tension while the casing is severed.

This invention relates to downhole equipment for use in the gas and oildrilling industry.

It is a frequent requirement of the gas and oil drilling industry to cutand remove sections of a wellbore casing. Typically, a casing cutterhaving extendable cutting blades is run into the wellbore and locatedadjacent the section of casing to be severed. The cutter is rotated andthe cutting blades extended so as to engage the inner casing surface.Extension of the cutting blades continues until the blades completelypenetrate the casing to create two separate casing portions. The upholecasing portion may be then removed from the wellbore as necessary.

On occasions, there is also a requirement to cut a wellbore casingwhilst maintaining the portion of casing located below the cut in astate of tension. However, adequate means for satisfying thisrequirement has not previously been available.

It is an object of the present invention to provide apparatus forallowing a casing to be severed whilst maintaining a portion of casingbelow the region of severing in a state of tension.

It is a further object of the invention to provide such apparatus whichis also compatible with a conventional casing cutter.

The invention provides apparatus for use in a wellbore, the apparatuscomprising a first elongate member provided with at least one tooth, asecond elongate member provided with at least one tooth; the first andsecond elongate members being arranged in telescopic relation to oneanother so as to be moveable relative to one another in a longitudinaldirection between a retracted position, in which the at least one toothof the first elongate member is engaged with the at least one tooth ofthe second elongate member so as to prevent relative rotation betweensaid elongate members, and au extended position, in which the at leastone tooth of the first elongate member is completely disengaged from theat least one tooth of the second elongate member so as to permit relaterotation between said elongate members and abutment surfaces of saidelongate members are in mechanical communication with each other so asto prevent further extending longitudinal movement of said elongatemembers and thereby permit the transmission of a tension force throughthe apparatus via mean provided on each of the first and second elongatemembers for connecting said members, when in use, to additionalapparatus.

In use, a conventional casing cutter may be attached uphole of theaforementioned apparatus (a “tension swivel sub”) to one of the elongatemembers (e.g the first elongate member) whilst a casing spear isattached downhole of the apparats to the other of the elongate members(e.g. the second elongate member). The resultant cutting sting may bethen run into a wellbore and located at the required depth. The casingspear may be set by means of an appropriate string rotation which istransmitted to the spear through the engagement of the elongate memberteeth. Once the spear has been set so as to grip the wellbore casing, anuphole force may be applied to the string which moves the elongatemember from the retracted position to the extended position. Theabutment surfaces of the elongate members are thereby placed inmechanical communication with each other, and as a result, the upholeforce places the region of casing located below the spear in a state oftension. Furthermore, movement of the elongate members into the extendedposition disengages the teeth thereby allowing free rotation of theelongate member attached to the casing cutter and the cutting stringlocated thereabove. Thus, the casing cutter may be then rotated so as tosever the wellbore casing. Once the cutting operation has beencompleted, the uphole force on the cutting string, and accordingly thetension in the casing below the spear, may be slowly reduced to zero.The teeth of the elongate members are then re-engaged so as to permitrotation of the elongate member attached to the spear and therebyrelease the spear from the wellbore casing.

Preferably, biasing means is provided to bias the first and secondelongate members into the retracted position. The biasing means isideally a spring which may be located between the abutment surfaces ofsaid elongate members. It is preferable for the spring to havesufficient stiffness to maintain the elongate members in the retractedposition when, during use, the apparatus is placed in a state of tensiondue to the suspension of downhole equipment from said apparatus.Furthermore, a bearing is preferably located between the abutmentsurfaces of said elongate members. The first and second elongate membersare preferably each provided with a multiplicity of teeth.

Thus, the apparatus of the invention provides means for setting a spearand for holding a casing and cutting sting in tension while the casingis severed above the spear by means of a conventional rotary casingcutter. Furthermore, once the casing has been cut, the tension in thecasing and cutting string may be reduced in a controlled mariner and thespear may be thereby conveniently released.

An embodiment of the present invention will now be described withreference to the accompanying drawings, in which:

FIG. 1 is a schematic view of apparatus according to the inventionlocated in a wellbore in combination with a casing cutter and spear;

FIG. 2 is a detailed view of apparatus according to the invention incombination with a conventional rotary casing cutter and spear; and

FIG. 3 is a cross-section view of apparatus according to the invention.

Referring to FIG. 1, apparatus according to the invention (a tensionswivel sub 2) is shown located in a wellbore casing 60 with aconventional rotary casing cutter 70 and a conventional spear 80. Thecasing cutter 70 is positioned uphole of the swivel sub 2 and comprisescutter blades 72 which may be extended from a stored position so as toengage the adjacent region of wellbore casing and, through rotation ofthe cutting string, sever said region of the casing. This operation iswell known to those skilled in the art The spear 80 is positioneddownhole of the swivel sub 2 and engages the wellbore casing 60 so thatan uphole force may be applied to a portion of casing located below theline of severing. The purpose of the swivel sub 2 is to provide meansfor setting and unsetting the spear and to allow an uphole force to beapplied to the set spear whilst allowing rotary operation of the casingcutter. A more detailed view of the casing cutter 70, the swivel sub 2and the spear 80 is provided in FIG. 2. The casing cutter 70 and spear80 are both of a conventional design and their operation will be readilyunderstood by the skilled person. Consequently, detailed discussion ofthese items of equipment will not be presented.

Referring to FIG. 3, the tension swivel sub 2 has a body 4 which is of agenerally cylindrical shape with connecting means 6,8 provided at eitherend. The connecting means 6 provided at the downhole end of the body 4is in the form of a male connector having external screw threads 10 forinterengagement with an assembly downhole of the swivel sub 2. Incontrast, the connecting means 8 located at the uphole end of the body 4is in the form of a female connector having internal screw threads 12for interengagement with an assembly uphole of the swivel sub 2.

The body 4 is made up of a drive sub 14, a driven sub 16, an annulardrive sleeve 18, a driven mandrel 20 and a number of additionalcomponents assisting and controlling relative movement between theaforementioned driving and driven elements.

The drive sub 14 is generally cylindrical in shape and at the uphole endthereof is integrally provided with the female connecting means 8. Thedownhole end of the drive sub 14 is provided with external screw threads22 for interengagement with corresponding internal screw threads 24provided on the uphole end of the annular drive sleeve 18.

The annular drive sleeve 18 is cylindrical in shape and is provided withan internal shoulder 26 at the downhole end thereof. The shoulder 26 hasthe function of applying a compression force on a compression spring 28.The downhole end of the annular drive sleeve 18 is also provided with amultiplicity of teeth 30. The teeth 30 extend longitudinally from thedownhole end of the sleeve 18 and each tooth is configured so as to havea leading face 32 lying in the same plane as that in which the centrallongitudinal axis of the swivel sub 2 lies. Each tooth of themultiplicity of teeth 30 is further configured to have a trailing face34 positioned at approximately 45° to the leading face 32 and to havethe shape of a right angled triangle with opposite and adjacent sides ofthe same length.

The inner surface of the drive sleeve 18 located between the internalshoulder 26 and the multiplicity of teeth 30 is provided with a recess36 for receiving a radial bearing 38. The radial bearing 38 engages theexternal surface of the driven mandrel 20 so as to assist relativerotational movement between the mandrel 20 and the sleeve 18. The drivenmandrel 20 is provided with an external shoulder 40 which is located atthe upbole end thereof and is adapted to apply a compression force onthe compression spring 28. The drive sleeve 18 and driven mandrel 20 aredimensioned so that the sleeve internal shoulder 26 extends radially tothe external surface of the mandrel 20 and so that the mandrel externalshoulder 40 extends radially to the internal surface of the sleeve 18.The arrangement is such that relative rotational and longitudinalmovement between the sleeve 18 and the mandrel 20 may occur withoutexcessive undesirable movement in a transverse direction whicheffectively generates a bend in the tension swivel sub 2.

Furthermore, the arrangement of the sleeve 18 and the mandrel 20provides a spring chamber 42 for the housing of the compression spring28, an extension arrester 44 and a thrust bearing assembly 46. Thecompression spring 28 locates within the spring chamber 42 so as todirectly contact the shoulder 40 of the mandrel 20. The downhole end ofthe spring 28 abuts a downhole end of the extension arrester 44 whichreacts spring force to the sleeve internal shoulder 26 by means of thethrust bearing assembly 46 located therebetween. The primary function ofthe thrust bearing assembly 46 is to assist the rotation of the drivencomponents (i.e. the mandrel 20 and the driven sub 16) relative to thedriving components (i.e. the sleeve 18 and the drive sub 14).

The downhole end of the mandrel 20 is provided with external screwthreads 48 for interengagement with corresponding internal screw threads50 provided on the driven sub 16. The driven sub 16 is generallycylindrical in shape and at the downhole end thereof is integrallyprovided with the male connecting means 6. The uphole end of the drivensub 16 is provided with a multiplicity of teeth 52 adapted forinterengagement with the multiplicity of teeth 30 provided on theannular drive sleeve 18. Each tooth of the multiplicity of teeth 52provided on the driven sub 16 has an identical shape, but reverseorientation, to each tooth of the sleeve 18. With the two sets of teeth30,52 interengaged, the uphole end of the mandrel 20 locates adjacentthe downhole end of the drive sub 14. It is preferable, however, thatthe mandrel 20 and drive sub 14 do not abut one another. In this way,the two sets of teeth 30,52 are firmly pressed together by means of thecompression spring 28 and excessive relative rotational movement at theteeth 30,52 interface is minimised.

The extension arrester 44 is configured so as to allow sufficient axialmovement of the driven components relative to the driving components toensure complete disengagement of the two sets of teeth 30,52. However,excessive relative axial movement is prevented through abutment of anuphole end of the extension arrester 44 with the mandrel externalshoulder 40. In this way, excess movement over that necessary todisengage the teeth 30,52 is prevented. Such excess movement couldpotentially render the tension swivel sub 2 vulnerable to undesirablebending. The mandrel external shoulder 40 shown in FIG. 3 has a steppedsurface 54 which provides positive location for the uphole end of thecompression spring 28.

In use, the casing cutter 70 is attached to the drive sub 14 by mean ofthe female connecting means 8. The casing spear 80 is attached to thedriven sub 16 by means of the male connecting means 6. The resultantstring is then run into a wellbore and located at the required depth.Although the spear 80 is suspended from the driven sub 16, thecompression spring 28 has sufficient stiffness to maintain the two setsof teeth 30,52 in firm engagement with each other. The casing spear 80is set by means of an appropriate rotation of the string. This rotationis transmitted to the spear via the engaged sets of teeth 30,52. Oncethe spear 80 has been set so as to grip the wellbore casing 60, anuphole force is applied to the string which is sufficient to move thedriving and driven components from a retracted position (in which thetwo sets of teeth 30,52 are firmly engaged) to an extended position (inwhich the uphole end of the arrester 44 is in abutment with the mandrelexternal shoulder 40). Thus, the uphole force places the region ofcasing located below the spear 80 in a state of tension. Furthermore,movement of the driving and driven components into the extended positionallows free rotation of the driving components and the string locatedthereabove. The casing cutter 70 is then rotated so as to sever thewellbore casing 60. Once the cutting operation has been completed, theuphole force on the string, and accordingly the tension in the casingbelow the spear 80, is slowly reduced to zero. The two sets of teeth30,52 re-engage as a result and the driven sub 16 is rotated so as torelease the spear 80. The casing cutter 70, the tension swivel sub 2,and the casing spear 80 may be then removed from the wellbore.

The present invention is not limited to the specific embodimentdescribed above. Alternative arrangements will be apparent to a readerskilled in the art. The swivel sub 2 illustrated in FIG. 3 is notprovided with a throughbore suitable for the circulation of wellborefluid. However, such a throughbore may be conveniently defined asrequired. Similarly, passages and tubing for hydraulic actuating fluidmay be extended through tile swivel sub 2 (for example, along thelongitudinal axis of the swivel sub 2) as necessary. As a furthervariation, the swivel sub 2 may be provided with biasing means in theform of a gas compression chamber rather than a coil compression spring.

What is claimed is:
 1. Apparatus for use in a wellbore comprising: afirst elongate member provided with at least one tooth; a secondelongate member provided with at least one tooth; the first and secondelongate members being arranged in telescopic relation to one another soas to be moveable relative to one another in a longitudinal directionbetween a retracted position in which the at least one tooth of thefirst elongate member is engaged with the at least one tooth of thesecond elongate member so as to prevent relative rotation between saidelongate members, and an extended position in which the at least onetooth of the first elongate member is completely disengaged from the atleast one tooth of the second elongate member so as to permit relativerotation between said elongate members and in which abutment surfaces ofsaid elongate members are in mechanical communication with each other soas to prevent further extending longitudinal movement of said elongatemembers and thereby permit the transmission of a tension force throughthe apparatus via means provided on each of the first and secondelongate members for connecting said members, when in use, to additionalapparatus.
 2. Apparatus as claimed in claim 1, including biasing meansto bias the first and second elongate members into the retractedposition.
 3. Apparatus as claimed in claim 2, wherein the biasing meansis a spring located between the abutment surfaces of said elongatemembers.
 4. Apparatus as claimed in claim 3, wherein the spring hassufficient stiffness to maintain the elongate members in the retractedposition when, during use, the apparatus is placed in a state of tensiondue to the suspension of downhole equipment from said apparatus. 5.Apparatus as claimed in claim 3 or 4, wherein a bearing is locatedbetween the abutment surfaces of said elongate members.
 6. Apparatus asclaimed in claim 1, wherein means for cutting a wellbore casing isconnected to the first elongate member.
 7. Apparatus as claimed in claim1, wherein means for gripping a wellbore casing is connected to thesecond elongate member.